Camshaft phasers are used in modern internal combustion engines to optimize fuel-economy figures and performance data. They serve to variably adjust the opening and closing times of the gas-exchange valves. For that purpose, the camshaft phaser has a stator driven by the crankshaft and a rotor connected to the camshaft for co-rotation therewith. Between the rotor and the stator, working chambers are provided that are able to be acted upon by a pressure medium and that are subdivided by vanes associated with the rotor into reciprocally acting pressure chambers. During operation of the internal combustion engine, both pressure chambers are permanently filled with pressure medium, so that the rotor and the stator are interconnected relatively stiffly. The timing of the gas-exchange valves is then thereby varied by increasing the pressure prevailing in one of the pressure chambers, while decreasing the pressure in the respective other pressure chamber. This requires supplying the pressure medium to the one pressure chamber and conducting it away from the other pressure chamber. To ensure that the system is not set into vibration, the inflow of the pressure medium must generally be controlled by the outflow thereof.
During engine start, the situation can occur where both pressure chambers are only partially filled with pressure medium since the camshaft phaser can drain itself independently via leakage sites. During this time period, the rotor is not hydraulically clamped in the camshaft phaser, so that it can vibrate uncontrollably. To avoid this effect, camshaft phasers are already equipped with a mechanical locking system that couples the rotor to the stator via a fixed mechanical connection. To ensure that the rotor is reliably locked, the locking position corresponds to the limit stop of the rotor relative to the stator either in the timing advance or the timing retard direction.
The German Patent Application DE 10 2008 052 275 A1 describes a camshaft phaser having two hydraulically actuatable locking devices, where the rotor can be locked in a middle position relative to the stator. This requires providing additional pressure medium channels in the camshaft phaser.
In the case of such a camshaft phaser, the relatively costly pressure medium circuit thereof presents a problem that is to be generally resolved. The pressure medium channels must essentially extend over a certain extent in order to form suitable control edges and convey the pressure medium, whereby an installation space problem can arise, in particular at constrictions, since, in any case, the pressure medium channels must be separate from one another to prevent any short-circuiting.